A patient’s resting Frank-Starling curve is shown below and denoted as Curve 1. Which of the following scenarios would cause the patient’s Frank-Starling curve to more closely resemble that denoted by Curve 2?

A. Heart failure
B. Propranolol administration
C. Dilated cardiomyopathy
D. Dobutamine administration
E. Myocardial infarction
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 1 Question is…
D. Dobutamine administration
Before we get to the main explanation, let’s look at the explanations for the incorrect answers. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
A. Heart failure
Incorrect: Heart failure would result in reduced cardiac contractility, which would shift the curve downwards and to the right. In contrast, this question is looking for a factor that would shift the curve upwards and to the left.
B. Propranolol administration
Incorrect: Propranolol is a β-blocker that reduces cardiac contractility, which shifts the curve downwards and to the right. In contrast, this question is looking for a factor that would shift the curve upwards and to the left.
C. Dilated cardiomyopathy
Incorrect: Dilated cardiomyopathy is a condition wherein the heart becomes enlarged and cannot pump blood effectively. The condition would result in reduced cardiac contractility, which would shift the curve downwards and to the right. In contrast, this question is looking for a factor that would shift the curve upwards and to the left.
E. Myocardial infarction
Incorrect: A myocardial infarction can lead to cardiac tissue injury and death. These changes would likely result in reduced cardiac contractility and cause the Frank-Starling curve to shift downwards and to the right.
Main Explanation
The Frank-Starling mechanism describes the relation between end-diastolic volume (EDV) and stroke volume (SV).
Factors that increase cardiac contractility, also known as inotropy, cause the curve to shift upwards and to the left. Examples of such factors include exercise, increased catecholamine release (e.g., fight-or-flight response), and inotropic medications (e.g., dobutamine, milrinone, and digoxin).
In contrast, factors that decrease cardiac contractility will cause the curve to shift downwards and to the right. Examples of such factors include heart failure, loss of functional myocardium (e.g. myocardial infarction), dilated cardiomyopathy, and medications that decrease inotropy (e.g., β-blockers, calcium channel blockers).

Major Takeaway
The Frank-Starling mechanism describes the relation between end-diastolic volume and stroke volume. Factors that increase cardiac contractility will lead to an upward and leftward shift of the curve. In contrast, factors that decrease cardiac contractility will lead to a downward and rightward shift of the curve.

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